Devices that are used in downhole environments tend to experience corrosion or wear due to the various conditions of the downhole environment, such as elevated temperatures, elevated pressures and the various chemicals found therein. Knowing how well a material can withstand the effects of the downhole environment can be informative when designing tools and components for downhole applications. Therefore, experiments are generally designed in which test objects are immersed in fluids obtained from downhole and pressures and temperatures are raised to reasonably simulate a downhole environment. Unfortunately, vessels for containing the test object need to be sealed to sufficiently maintain downhole conditions in the pressure vessel during the measurement process. The present disclosure provides a method and apparatus for sealing a pressure vessel to maintain downhole pressures within the pressure vessel.